Transport of opened cotton tufts or fibers in moving air currents is old in the art, as is the separation of the cotton from the air by passing the air through a condenser screen which retains the cotton fibers and permits the air to pass on. While it may be necessary to transport the fibers in air currents moving at around 2,000 feet per minute in a duct, the condenser screen normally has a large area in comparison with the cross-section of the dust, so that air velocity through the screen and fiber impingement velocity against the screen are notably lower than the air velocity in the duct. Some cotton dust and trash may be shaken from the fibers to pass on with the air currents, but the mat of fibers on the condenser will form a filter to a certain extent, and much of the dust will remain in the mat and loose dust in the air stream may even be filtered out onto the mat.
In many cases, filters are employed to remove airborne fibers and dust from the ambient air in cotton mills, and the air velocity through the filter medium is normally restricted to about 200 feet per minute so that both the fibers and the dust will be retained on the filter medium. Often the buildup of a mat of fibers on the filter medium to a thickness of three or four inches is used as an additional filtration means or filter medium to prevent the dust from passing on through with the air currents. Therefore, the usual condenser or filter is a dust retainer, not a dust remover.
Typical of the prior art in U.S. Pat. No. 1,593,965, which discloses an apparatus for shaking dust from cotton or other fibers during airborne transport by impinging the fibers obliquely against a screen to shake dust from the fibers and allow it to pass by momentum through the screen along with some of the air, while the main stream of air and the usable fibers are deflected and pass on beyond the screen. Since this apparatus is intended for insertion into the conventional airborne transport duct of a fiber processing plant, conventional air velocities combined with suitable low angles of obliquity have the result that "loss due to particles adhering to the screen will be minimized and at the same time the material is permitted to impinge upon the screen with sufficient force to partly loosen the dust" according to the patent.
Another example of the prior art is U.S. Pat. No. 2,813,306, which discloses a rotating condenser screen for forming a mat of fibers on the outside thereof, with rotating paddles in close proximity to the inside surface of the screen rotating at a speed suitable to create reverse air flow through the screen ahead of the paddles, thereby lifting the mat from the screen momentarily at the passage of each paddle and flapping it back down thereafter to shake dust from the mat of fibers into the airstream passing through the condenser. As a practical matter, it appears that the air velocity through the condenser would be restricted to a few hundred feet per minute if the paddle wheel is to run at a practical speed.
Various combinations of physical beaters, deflections of direction, grid screens, condensers, etc., have been used historically in cotton opening and cleaning machinery, but the end porduct still contains objectionable amounts of healthaffecting respirable dust, currently defined by the U.S. Government as having 15 micron particle size or less, and leaf or other trash and dust of larger size, all detrimental to the operation of open-end yarn spinning equipment as well.
The apparatus of the present invention operates in a different environment, and in a different order of magnitude as to air velocities, in order to both shake and pull respirable dust from opened tufts of cotton fibers which have already experienced the conventional opening and cleaning processes, and incidentally removing large quantities of larger dust and trash particles. This apparatus not only removes significant quantities of dust and trash, but also delivers the fibers in an improved state of openness and regularity, to the benefit of the health of cotton mill employees and to the efficiency of operation of spinning equipment, particularly open-end spinning equipment which is sensitive to the presence of dust and trash in the fibers spun.